There have recently been proposals to allow access to the features and services provided by cellular networks, such as GSM, 3G/UMTS, CDMA2000 and WiMax networks, other than by accessing those networks in the conventional manner. In this regard, the conventional manner is by signaling between a mobile terminal and a conventional base station (macro base station) that has a dedicated connection to a Mobile Switching Centre (MSC), and which provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. GSM, UMTS etc) communication transport protocols. It has been proposed to increase network capacity by providing additional special base stations, referred to as access points (APs), for example at a subscriber's home or office. Many different names have been given to APs, such as home access points (HAPs), micro-base stations, pico-base stations, pico-cells and femto-cells, but all names refer to the same apparatus. APs provide short range, localized cellular telecommunications coverage, and are typically purchased by, or rented to, a subscriber to be installed in their house or business premises.
These APs may be dedicated network access points, or may be enhanced wireless internet hubs (i.e. providing wireless internet access, as well as wireless telecommunications network access). The range of APs is significantly smaller than macro base stations, typically only providing coverage of the order of 20 to 30 meters.
It has also been proposed to use APs in the Long Term Evolution (LTE) telecommunications network currently being developed, but not yet implemented. LTE is likely to be the next network implementation after 3G/UMTS. Overall, the system described herein is applicable to any type of cellular telecommunications system, including GSM, 3G/UMTS, LTE, CDMA2000 and WiMax.
There are several potential advantages of introducing APs in existing telecommunications networks including reducing capacity on macro networks by routing calls through DSL infrastructure, improving indoor coverage by the dedicated APs and, where sufficient numbers of APs are implemented, the power level of the macro coverage could be reduced, due to a lower demand for the macro-base stations and the fact that the signals from the macro-base stations will not need to penetrate into buildings and areas covered by the APs. Power reductions of course result in energy and financial savings, for instance due to less spectrum being required and also less hardware.
A further advantage of using an access point connected to the core network via an IP network is that existing broadband Digital Subscriber Line (DSL) connections can be used to link mobile terminals with the network core without using the capacity of the radio access network or transmission network of a mobile telecommunications network. In other words, the AP is connected to or integrated into a DSL modem/router and uses DSL to backhaul the traffic to the communication network.
A still further advantage is that APs are able to provide mobile network access to areas where there is no macro radio access network coverage. For example, an AP could provide 3G coverage in an area where there is no macro 3G coverage at all, perhaps only macro GSM coverage. The use of APs as an additional or alternative means for accessing the network therefore advantageously increases the network capacity.
Currently, telecommunication network providers sometimes offer subscribers different call tariffs based on their location. For instance, one such service provides subscribers with cheaper tariffs when they use their mobile terminal in their home.
APs provide another opportunity for network providers to offer reduced rates to subscribers. For instance, subscribers may benefit from a different call tariff when using their mobile terminal through an AP acting as a base station. Such a tariff may be described as a “Homezone” tariff.
For all of the above reasons, it is beneficial that networks know where to expect the AP to be located. Typically, on sale or installation of an AP, the customer would be asked to confirm the location at which he will be installing his AP. The AP will then be registered at this location.
APs are expected to be small, light units which are plugged into DSL. Further additional challenges arise in implementing these access points as conventional base stations in view of their potential mobility. Ideally APs are introduced into a telecommunications network and remain fixed at that site. However, there is the possibility that subscribers may decide to relocate their access point for use at a different site. This would be problematic where the subscriber obtains a reduced tariff for using their AP as a base station from their home, as potentially they would be able to also receive the reduced tariff at other locations by relocating the AP. There is therefore the need for determining the location of an AP in order to determine whether or not a reduced tariff is to be used.
A further problem in regard to the mobility of APs is that mobile telecommunication providers are allocated spectrum in specific regions, so it is vital that they are able to identify the location of all their base stations, which includes APs, since APs are functionally equivalent to macro base stations. In fact, proposed regulatory regulations are likely to require telecommunications providers to know the location of all access points in their network. There is therefore also a need to determine the location of an AP before allowing a communication to proceed. Where a femtocell is determined to be outside the licensed area, it is envisaged that the femtocell radio transmitter would be deactivated.
Further reasons for controlling mobility of APs are to enable emergency calls to be routed to an appropriate local emergency call centre. Also, knowledge of location of APs through which calls are made can be useful in police investigations.
In International Application No. PCT/GB2007/004007, published as WO 2008/047140 A1, which is incorporated herein by reference, there is described a means for identifying the location of an access point by checking the DSL ID of the DSL line into which the access point is connected or by checking the CLI of the line into which the access point is connected.
Accordingly, it would be desirable to provide an alternative, or additional, method which can detect if an access point has moved to an unauthorised location.